The present invention relates to semiconductor laser devices and methods for fabricating the devices, and more particularly relates to semiconductor laser devices which are used as a light source for the reading or writing of data from or on optical storage mediums such as compact discs and digital versatile discs, and methods for fabricating the devices.
Typical digital-versatile-disc (hereinafter referred to as “DVD”) players need to function to play back compact discs (hereinafter referred to as “CDs”) in addition to DVDs, and also have to function to replay, and store data on, recordable CDs (CD-Rs) which have become widespread rapidly in recent years.
As a light for replaying DVDs, a red laser beam with a wavelength in the 650 nm band is employed, while an infrared laser beam with a wavelength in the 780 nm band is used as a light for playing back CDs and CD-R discs. In the currently available DVD players, therefore, two semiconductor laser diodes are incorporated: one is a red semiconductor laser diode for generating a red laser beam and the other is an infrared semiconductor laser diode for generating an infrared laser beam.
With an increasing demand for smaller personal computers and other information equipment, DVD players also need to be reduced further in size and thickness. To that end, it is indispensable to reduce the size and thickness of optical pickup. Methods for reducing optical pickup in size and thickness include optical system simplification.
As a method for simplifying an optical system, integration of a red semiconductor laser diode and an infrared semiconductor laser diode is available. The current DVD players include two optical systems: one for a red semiconductor laser diode and the other for an infrared semiconductor laser diode. Integration of the red semiconductor laser diode and the infrared semiconductor laser diode allows one optical system to be shared, thereby realizing an optical pickup system of smaller size and thickness.
For instance, as one example of the integration of a red semiconductor laser diode and an infrared semiconductor laser diode, a so-called monolithic semiconductor laser diode array which is integrated on a substrate is disclosed in Japanese Laid-Open Publication No. 11-186651.
Japanese Laid-Open Publication Nos. 11-144307 and 11-149652 disclose another example, in which hybrid integration of two semiconductor laser chips, one for a red laser and the other for an infrared laser, enables an optical system to be shared in an optical pickup system.
Nevertheless, in the conventional monolithic two-wavelength laser diode array, the respective active layers of the laser diodes have different compositions and thus have to be grown in different process steps, which results in the problem of low yields. In particular, when high-output laser diodes are monolithically integrated, yields decrease significantly.
Moreover, it is very difficult, in the viewpoint of crystal growth, to monolithically integrate a gallium nitride (GaN)-based blue laser diode, which is used in high density DVDs, and an aluminum gallium indium phosphide (AlGaInP)-based red laser diode, which is used in typical (conventional) DVDs.
The conventional hybrid optical pickup, on the other hand, have the problem that when the red semiconductor laser chip and the infrared semiconductor laser chip are assembled using assembly equipment, it is difficult to control and optimize the locations of active layers of the semiconductor laser chips and the distance between the light emitting points thereof.
In recent years, mounting methods in which a fluidic self-assembly (hereinafter referred to as “FSA”) technique is used have been developed as one type of device-mounting method.
In the FSA technology, devices (hereinafter referred to as “function blocks”) ranging in size from 10 μm to several hundred μm and having given shapes are suspended into a liquid to form a slurry. The liquid (suspension) in the form of slurry is poured over the surface of a substrate in which recessed portions have been formed. The recessed portions are substantially the same as the function blocks in size and shape. In this manner, the function blocks that have been spread in the liquid are settled into the recessed portions and thereby mounted onto the substrate.
The FSA technology is disclosed in U.S. Pat. No. 5,545,291, U.S. Pat. No. 5,783,856, U.S. Pat. No. 5,824,186 and U.S. Pat. No. 5,904,545, for example.